<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html lang="en">
<head>
<title>Source code</title>
<link rel="stylesheet" type="text/css" href="../../../../../stylesheet.css" title="Style">
</head>
<body>
<div class="sourceContainer">
<pre><span class="sourceLineNo">001</span>/*<a name="line.1"></a>
<span class="sourceLineNo">002</span> * Copyright (C) 2007 The Guava Authors<a name="line.2"></a>
<span class="sourceLineNo">003</span> *<a name="line.3"></a>
<span class="sourceLineNo">004</span> * Licensed under the Apache License, Version 2.0 (the "License");<a name="line.4"></a>
<span class="sourceLineNo">005</span> * you may not use this file except in compliance with the License.<a name="line.5"></a>
<span class="sourceLineNo">006</span> * You may obtain a copy of the License at<a name="line.6"></a>
<span class="sourceLineNo">007</span> *<a name="line.7"></a>
<span class="sourceLineNo">008</span> * http://www.apache.org/licenses/LICENSE-2.0<a name="line.8"></a>
<span class="sourceLineNo">009</span> *<a name="line.9"></a>
<span class="sourceLineNo">010</span> * Unless required by applicable law or agreed to in writing, software<a name="line.10"></a>
<span class="sourceLineNo">011</span> * distributed under the License is distributed on an "AS IS" BASIS,<a name="line.11"></a>
<span class="sourceLineNo">012</span> * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.<a name="line.12"></a>
<span class="sourceLineNo">013</span> * See the License for the specific language governing permissions and<a name="line.13"></a>
<span class="sourceLineNo">014</span> * limitations under the License.<a name="line.14"></a>
<span class="sourceLineNo">015</span> */<a name="line.15"></a>
<span class="sourceLineNo">016</span><a name="line.16"></a>
<span class="sourceLineNo">017</span>package com.google.common.collect;<a name="line.17"></a>
<span class="sourceLineNo">018</span><a name="line.18"></a>
<span class="sourceLineNo">019</span>import static com.google.common.base.Preconditions.checkState;<a name="line.19"></a>
<span class="sourceLineNo">020</span><a name="line.20"></a>
<span class="sourceLineNo">021</span>import com.google.common.annotations.GwtCompatible;<a name="line.21"></a>
<span class="sourceLineNo">022</span><a name="line.22"></a>
<span class="sourceLineNo">023</span>import java.util.NoSuchElementException;<a name="line.23"></a>
<span class="sourceLineNo">024</span><a name="line.24"></a>
<span class="sourceLineNo">025</span>/**<a name="line.25"></a>
<span class="sourceLineNo">026</span> * This class provides a skeletal implementation of the {@code Iterator}<a name="line.26"></a>
<span class="sourceLineNo">027</span> * interface, to make this interface easier to implement for certain types of<a name="line.27"></a>
<span class="sourceLineNo">028</span> * data sources.<a name="line.28"></a>
<span class="sourceLineNo">029</span> *<a name="line.29"></a>
<span class="sourceLineNo">030</span> * &lt;p&gt;{@code Iterator} requires its implementations to support querying the<a name="line.30"></a>
<span class="sourceLineNo">031</span> * end-of-data status without changing the iterator's state, using the {@link<a name="line.31"></a>
<span class="sourceLineNo">032</span> * #hasNext} method. But many data sources, such as {@link<a name="line.32"></a>
<span class="sourceLineNo">033</span> * java.io.Reader#read()}, do not expose this information; the only way to<a name="line.33"></a>
<span class="sourceLineNo">034</span> * discover whether there is any data left is by trying to retrieve it. These<a name="line.34"></a>
<span class="sourceLineNo">035</span> * types of data sources are ordinarily difficult to write iterators for. But<a name="line.35"></a>
<span class="sourceLineNo">036</span> * using this class, one must implement only the {@link #computeNext} method,<a name="line.36"></a>
<span class="sourceLineNo">037</span> * and invoke the {@link #endOfData} method when appropriate.<a name="line.37"></a>
<span class="sourceLineNo">038</span> *<a name="line.38"></a>
<span class="sourceLineNo">039</span> * &lt;p&gt;Another example is an iterator that skips over null elements in a backing<a name="line.39"></a>
<span class="sourceLineNo">040</span> * iterator. This could be implemented as: &lt;pre&gt;   {@code<a name="line.40"></a>
<span class="sourceLineNo">041</span> *<a name="line.41"></a>
<span class="sourceLineNo">042</span> *   public static Iterator&lt;String&gt; skipNulls(final Iterator&lt;String&gt; in) {<a name="line.42"></a>
<span class="sourceLineNo">043</span> *     return new AbstractIterator&lt;String&gt;() {<a name="line.43"></a>
<span class="sourceLineNo">044</span> *       protected String computeNext() {<a name="line.44"></a>
<span class="sourceLineNo">045</span> *         while (in.hasNext()) {<a name="line.45"></a>
<span class="sourceLineNo">046</span> *           String s = in.next();<a name="line.46"></a>
<span class="sourceLineNo">047</span> *           if (s != null) {<a name="line.47"></a>
<span class="sourceLineNo">048</span> *             return s;<a name="line.48"></a>
<span class="sourceLineNo">049</span> *           }<a name="line.49"></a>
<span class="sourceLineNo">050</span> *         }<a name="line.50"></a>
<span class="sourceLineNo">051</span> *         return endOfData();<a name="line.51"></a>
<span class="sourceLineNo">052</span> *       }<a name="line.52"></a>
<span class="sourceLineNo">053</span> *     };<a name="line.53"></a>
<span class="sourceLineNo">054</span> *   }}&lt;/pre&gt;<a name="line.54"></a>
<span class="sourceLineNo">055</span> *<a name="line.55"></a>
<span class="sourceLineNo">056</span> * This class supports iterators that include null elements.<a name="line.56"></a>
<span class="sourceLineNo">057</span> *<a name="line.57"></a>
<span class="sourceLineNo">058</span> * @author Kevin Bourrillion<a name="line.58"></a>
<span class="sourceLineNo">059</span> * @since 2.0 (imported from Google Collections Library)<a name="line.59"></a>
<span class="sourceLineNo">060</span> */<a name="line.60"></a>
<span class="sourceLineNo">061</span>// When making changes to this class, please also update the copy at<a name="line.61"></a>
<span class="sourceLineNo">062</span>// com.google.common.base.AbstractIterator<a name="line.62"></a>
<span class="sourceLineNo">063</span>@GwtCompatible<a name="line.63"></a>
<span class="sourceLineNo">064</span>public abstract class AbstractIterator&lt;T&gt; extends UnmodifiableIterator&lt;T&gt; {<a name="line.64"></a>
<span class="sourceLineNo">065</span>  private State state = State.NOT_READY;<a name="line.65"></a>
<span class="sourceLineNo">066</span><a name="line.66"></a>
<span class="sourceLineNo">067</span>  /** Constructor for use by subclasses. */<a name="line.67"></a>
<span class="sourceLineNo">068</span>  protected AbstractIterator() {}<a name="line.68"></a>
<span class="sourceLineNo">069</span><a name="line.69"></a>
<span class="sourceLineNo">070</span>  private enum State {<a name="line.70"></a>
<span class="sourceLineNo">071</span>    /** We have computed the next element and haven't returned it yet. */<a name="line.71"></a>
<span class="sourceLineNo">072</span>    READY,<a name="line.72"></a>
<span class="sourceLineNo">073</span><a name="line.73"></a>
<span class="sourceLineNo">074</span>    /** We haven't yet computed or have already returned the element. */<a name="line.74"></a>
<span class="sourceLineNo">075</span>    NOT_READY,<a name="line.75"></a>
<span class="sourceLineNo">076</span><a name="line.76"></a>
<span class="sourceLineNo">077</span>    /** We have reached the end of the data and are finished. */<a name="line.77"></a>
<span class="sourceLineNo">078</span>    DONE,<a name="line.78"></a>
<span class="sourceLineNo">079</span><a name="line.79"></a>
<span class="sourceLineNo">080</span>    /** We've suffered an exception and are kaput. */<a name="line.80"></a>
<span class="sourceLineNo">081</span>    FAILED,<a name="line.81"></a>
<span class="sourceLineNo">082</span>  }<a name="line.82"></a>
<span class="sourceLineNo">083</span><a name="line.83"></a>
<span class="sourceLineNo">084</span>  private T next;<a name="line.84"></a>
<span class="sourceLineNo">085</span><a name="line.85"></a>
<span class="sourceLineNo">086</span>  /**<a name="line.86"></a>
<span class="sourceLineNo">087</span>   * Returns the next element. &lt;b&gt;Note:&lt;/b&gt; the implementation must call {@link<a name="line.87"></a>
<span class="sourceLineNo">088</span>   * #endOfData()} when there are no elements left in the iteration. Failure to<a name="line.88"></a>
<span class="sourceLineNo">089</span>   * do so could result in an infinite loop.<a name="line.89"></a>
<span class="sourceLineNo">090</span>   *<a name="line.90"></a>
<span class="sourceLineNo">091</span>   * &lt;p&gt;The initial invocation of {@link #hasNext()} or {@link #next()} calls<a name="line.91"></a>
<span class="sourceLineNo">092</span>   * this method, as does the first invocation of {@code hasNext} or {@code<a name="line.92"></a>
<span class="sourceLineNo">093</span>   * next} following each successful call to {@code next}. Once the<a name="line.93"></a>
<span class="sourceLineNo">094</span>   * implementation either invokes {@code endOfData} or throws an exception,<a name="line.94"></a>
<span class="sourceLineNo">095</span>   * {@code computeNext} is guaranteed to never be called again.<a name="line.95"></a>
<span class="sourceLineNo">096</span>   *<a name="line.96"></a>
<span class="sourceLineNo">097</span>   * &lt;p&gt;If this method throws an exception, it will propagate outward to the<a name="line.97"></a>
<span class="sourceLineNo">098</span>   * {@code hasNext} or {@code next} invocation that invoked this method. Any<a name="line.98"></a>
<span class="sourceLineNo">099</span>   * further attempts to use the iterator will result in an {@link<a name="line.99"></a>
<span class="sourceLineNo">100</span>   * IllegalStateException}.<a name="line.100"></a>
<span class="sourceLineNo">101</span>   *<a name="line.101"></a>
<span class="sourceLineNo">102</span>   * &lt;p&gt;The implementation of this method may not invoke the {@code hasNext},<a name="line.102"></a>
<span class="sourceLineNo">103</span>   * {@code next}, or {@link #peek()} methods on this instance; if it does, an<a name="line.103"></a>
<span class="sourceLineNo">104</span>   * {@code IllegalStateException} will result.<a name="line.104"></a>
<span class="sourceLineNo">105</span>   *<a name="line.105"></a>
<span class="sourceLineNo">106</span>   * @return the next element if there was one. If {@code endOfData} was called<a name="line.106"></a>
<span class="sourceLineNo">107</span>   *     during execution, the return value will be ignored.<a name="line.107"></a>
<span class="sourceLineNo">108</span>   * @throws RuntimeException if any unrecoverable error happens. This exception<a name="line.108"></a>
<span class="sourceLineNo">109</span>   *     will propagate outward to the {@code hasNext()}, {@code next()}, or<a name="line.109"></a>
<span class="sourceLineNo">110</span>   *     {@code peek()} invocation that invoked this method. Any further<a name="line.110"></a>
<span class="sourceLineNo">111</span>   *     attempts to use the iterator will result in an<a name="line.111"></a>
<span class="sourceLineNo">112</span>   *     {@link IllegalStateException}.<a name="line.112"></a>
<span class="sourceLineNo">113</span>   */<a name="line.113"></a>
<span class="sourceLineNo">114</span>  protected abstract T computeNext();<a name="line.114"></a>
<span class="sourceLineNo">115</span><a name="line.115"></a>
<span class="sourceLineNo">116</span>  /**<a name="line.116"></a>
<span class="sourceLineNo">117</span>   * Implementations of {@link #computeNext} &lt;b&gt;must&lt;/b&gt; invoke this method when<a name="line.117"></a>
<span class="sourceLineNo">118</span>   * there are no elements left in the iteration.<a name="line.118"></a>
<span class="sourceLineNo">119</span>   *<a name="line.119"></a>
<span class="sourceLineNo">120</span>   * @return {@code null}; a convenience so your {@code computeNext}<a name="line.120"></a>
<span class="sourceLineNo">121</span>   *     implementation can use the simple statement {@code return endOfData();}<a name="line.121"></a>
<span class="sourceLineNo">122</span>   */<a name="line.122"></a>
<span class="sourceLineNo">123</span>  protected final T endOfData() {<a name="line.123"></a>
<span class="sourceLineNo">124</span>    state = State.DONE;<a name="line.124"></a>
<span class="sourceLineNo">125</span>    return null;<a name="line.125"></a>
<span class="sourceLineNo">126</span>  }<a name="line.126"></a>
<span class="sourceLineNo">127</span><a name="line.127"></a>
<span class="sourceLineNo">128</span>  @Override<a name="line.128"></a>
<span class="sourceLineNo">129</span>  public final boolean hasNext() {<a name="line.129"></a>
<span class="sourceLineNo">130</span>    checkState(state != State.FAILED);<a name="line.130"></a>
<span class="sourceLineNo">131</span>    switch (state) {<a name="line.131"></a>
<span class="sourceLineNo">132</span>      case DONE:<a name="line.132"></a>
<span class="sourceLineNo">133</span>        return false;<a name="line.133"></a>
<span class="sourceLineNo">134</span>      case READY:<a name="line.134"></a>
<span class="sourceLineNo">135</span>        return true;<a name="line.135"></a>
<span class="sourceLineNo">136</span>      default:<a name="line.136"></a>
<span class="sourceLineNo">137</span>    }<a name="line.137"></a>
<span class="sourceLineNo">138</span>    return tryToComputeNext();<a name="line.138"></a>
<span class="sourceLineNo">139</span>  }<a name="line.139"></a>
<span class="sourceLineNo">140</span><a name="line.140"></a>
<span class="sourceLineNo">141</span>  private boolean tryToComputeNext() {<a name="line.141"></a>
<span class="sourceLineNo">142</span>    state = State.FAILED; // temporary pessimism<a name="line.142"></a>
<span class="sourceLineNo">143</span>    next = computeNext();<a name="line.143"></a>
<span class="sourceLineNo">144</span>    if (state != State.DONE) {<a name="line.144"></a>
<span class="sourceLineNo">145</span>      state = State.READY;<a name="line.145"></a>
<span class="sourceLineNo">146</span>      return true;<a name="line.146"></a>
<span class="sourceLineNo">147</span>    }<a name="line.147"></a>
<span class="sourceLineNo">148</span>    return false;<a name="line.148"></a>
<span class="sourceLineNo">149</span>  }<a name="line.149"></a>
<span class="sourceLineNo">150</span><a name="line.150"></a>
<span class="sourceLineNo">151</span>  @Override<a name="line.151"></a>
<span class="sourceLineNo">152</span>  public final T next() {<a name="line.152"></a>
<span class="sourceLineNo">153</span>    if (!hasNext()) {<a name="line.153"></a>
<span class="sourceLineNo">154</span>      throw new NoSuchElementException();<a name="line.154"></a>
<span class="sourceLineNo">155</span>    }<a name="line.155"></a>
<span class="sourceLineNo">156</span>    state = State.NOT_READY;<a name="line.156"></a>
<span class="sourceLineNo">157</span>    return next;<a name="line.157"></a>
<span class="sourceLineNo">158</span>  }<a name="line.158"></a>
<span class="sourceLineNo">159</span><a name="line.159"></a>
<span class="sourceLineNo">160</span>  /**<a name="line.160"></a>
<span class="sourceLineNo">161</span>   * Returns the next element in the iteration without advancing the iteration,<a name="line.161"></a>
<span class="sourceLineNo">162</span>   * according to the contract of {@link PeekingIterator#peek()}.<a name="line.162"></a>
<span class="sourceLineNo">163</span>   *<a name="line.163"></a>
<span class="sourceLineNo">164</span>   * &lt;p&gt;Implementations of {@code AbstractIterator} that wish to expose this<a name="line.164"></a>
<span class="sourceLineNo">165</span>   * functionality should implement {@code PeekingIterator}.<a name="line.165"></a>
<span class="sourceLineNo">166</span>   */<a name="line.166"></a>
<span class="sourceLineNo">167</span>  public final T peek() {<a name="line.167"></a>
<span class="sourceLineNo">168</span>    if (!hasNext()) {<a name="line.168"></a>
<span class="sourceLineNo">169</span>      throw new NoSuchElementException();<a name="line.169"></a>
<span class="sourceLineNo">170</span>    }<a name="line.170"></a>
<span class="sourceLineNo">171</span>    return next;<a name="line.171"></a>
<span class="sourceLineNo">172</span>  }<a name="line.172"></a>
<span class="sourceLineNo">173</span>}<a name="line.173"></a>




























































</pre>
</div>
</body>
</html>
